Half-bridge converters are often attractive for medium-power power supplies because of their ability to provide zero-voltage turn-on for the primary switches. The rectifier diodes, or blocking diodes, in a half-bridge converter, however, can be responsible for energy loss and voltage ringing due to the reverse recovery of the blocking diodes, since the blocking diodes often have to block a higher voltage than the blocking diodes of full-bridge converters. This can be particularly true in asymmetric half-bridge converters, where one of the blocking diodes can be forced to block a comparably much higher voltage. Snubber circuits are usually required to reduce the voltage ringing. Simple RC (resistor/capacitor) or RCD (resistor/capacitor/diode) snubbers have too much power loss, since any energy received by the snubber is dissipated in the resistor. Saturable inductors can be used to limit the di/dt through the diodes, and thus reduce the reverse recovery energy. Saturable inductors, however, present thermal management problems at high ambient temperatures.
Asymmetric half-bridge converters present additional difficulties for snubber design because the two rectifier diodes in the output circuit have different voltages, and these voltages change with input voltage and switch duty cycles. A good snubber should be self-regulating, that is it should be able to track the voltage change of the diodes automatically, and thus change the clamping voltages accordingly. The automatic tracking of the clamp voltages can also eliminate the current overshoot due to the charging of the clamping capacitors. This aids current sensing at the output of the converter for current mode control and over-current protection. Additionally, the snubber is preferably composed of components with very low ESL (equivalent series inductance) in order to clamp the very fast rate rise of voltage due to the reverse recovery diode current.